The present invention relates to a circuit arrangement for protection against fault currents in connection with power supplies having energy storing means, more especially for use with frequency converters for the operation of three-phase motors, with two identical detector windings placed on two current supply lines so that by means of a differential current detector winding coupled with these detector windings a circuit breaker may be tripped when a given value is exceeded.
Fault currents occur in defective equipment with and without grounding and may present a hazard for the owner or operator. The occurrence of fault currents makes itself felt for example by the presence of different amperages in power supply lines which are otherwise symmetrically loaded.
Such circuit arrangements for protection against fault currents have been proposed for instance in the German unexamined specification Nos. 3,048,785 and 3,633,787. These known circuit arrangements are placed in the line supply leads of an item of electrical equipment and when a fault current occurs they interrupt one of the supply leads. Such known devices are not suited to use for protection against fault currents in connection with power supplies with an energy storage means since the energy storage means involves the danger that the load connected with the supply will still receive a hazardous voltage even after a switching down of the power supply so that such stored energy will cause the load to perform erratic movements. A known system for interrupting the supply of current to a DC power supply does not guarantee rapid switching off of the output voltage at the output, as for example at the output of a frequency converter, since a substantial amount of energy is stored in the intermediate circuit capacitor of the DC power supply. Completely regular or reproducible switching off of the device then leaves much to be desired and may be so poor that strict government regulations are not fulfilled or maximum safety standards are not met.